Such dental furnaces for firing and, if applicable, pressing dental restoration parts have been known for a long time. In such dental furnaces, a dental restoration part is, or a number of dental restoration parts are, subjected to firing process or a pressing process, which is controlled by a program in accordance with predetermined temperature and, if applicable, pressing profiles.
The quality of the dental restoration parts produced considerably depends on that the parameters intended and adapted to the dental restoration material present are exactly adhered to during the firing and, if applicable, the pressing process. These do not only include the temperature profile to be adhered to, but also, for instance, the pressure conditions existing during the firing cycle.
Such dental restoration parts include dental restoration parts to be produced out of plastics, of metals, of composites, and in particular also of ceramics or of combinations of these dental.
The materials to be processed, the size, as well as the number and shape of dental restoration parts to be produced simultaneously determine, among other things, the overall heat capacity of the dental restoration parts to be processed. Thus, an adaptation of the heating power can become necessary, for which purpose different processing programmes can be activated at these firing or pressing furnaces via an input device, in which programmes optimum operation parameters for the respective circumstances (material, size, etc.) are stored. By activating and starting the suitable processing programme, a firing process for achieving an optimum quality in the product is aimed at.
Such dental furnaces essentially include a furnace base on which the dental restoration parts to be fired are accommodated, if applicable inside a muffle, a furnace hood which accommodates, besides a thermal insulation, in most cases also the heating device (e.g. electric heating coils), and a control device with a display and input device connected to it. The control device further comprises a memory device in which the processing programmes are stored. The input device for its part can be combined partly with the display device in the form of a touch-sensitive display (touch screen) and can furthermore as well comprise buttons (“soft keys”) that are in a basically known fashion provided with a firm function or with a function changeable via the display.
Such a dental furnace is, for example, described in DE 197 54 077 B4. On a display device, parameters can be displayed both numerically and in differently coloured depictions of curves which can be overlaid on one another. Input is possible via buttons, which allows to modify a firing programme if necessary.
Moreover, it has been suggested lately to equip dental furnaces also with a camera which is preferably also sensitive for the IR spectrum, and thus be able to record the temperature of the objects to be fired already during their placement in the furnace too. This has the advantage, among others, that a rather precise recording of the actual temperature, for instance of the muffle which was pre-heated in a pre-heating furnace in advance, can be achieved. By taking into account the actual temperature of the muffle, the processing programme of the dental furnace selected, for instance a pressing programme, can then be adapted and thus an improved result can be achieved.
Such recording of temperature has been suggested in such a fashion that based on an absolute temperature of the muffle thus recorded, a correction of the firing parameters, such as, for example, the duration of pre-heating, can be made in order to be able to guarantee optimum processing parameters for the material to be processed in the subsequent processing step.
Despite the sometimes rather complex control of the furnace parameters during the firing process, which takes into account, besides the actual firing temperature (or the firing curve), the introduction temperature of the dental restoration parts to be fired as well as the specifics of the materials to be fired, it has turned out that the firing results and the quality, respectively, of the dental restorations thus manufactured do not always meet the expectations.